When you prepare a quote for a project, you should keep for yourself a list of the value of your first drafts, brainstorming, communication, revisions and final files. If this happens again, you'll know what you should charge.
It's hard to judge that situation, it depends on the contract.
But in general you should have something in it about cancelling projects. You can charge a minimum percentage even though the project is not completed; you can even charge an extra fee actually.
If you don't have anything in your contract about it, evaluate how
many hours you spent, including the communication, and then charge it
at hourly rate. That should work fine for now.
Note that if the client used YOUR files and modified them, that's legally not right unless you specified otherwise; usually that's your intellectual property until the work has been fully paid. If you have no mention of this anywhere on our contract or proofs, then add it for next time. And also, don't ever send vectors, high resolution or files easy to modify as proofs...
Your question also seem to indicate you didn't ask for a down payment! Be careful about this and make sure you split your quote into many payments along the way. It could happen one day a client will cancel and not even want to pay you, although it's rare.
I don't want to sound patronizing (but probably will), but yes it's unfortunately partly your fault if communication wasn't clear; you need to ask questions and take control when things are vague. Don't take all the blame though and feel ultra guilty, if you've worked with the client for 10 years, this is quite a weird situation and the client should know better too. That's why I think charging at hourly rate or a percentage of the work done is fair for both of you.
Ask precise questions if you want precise answers, give examples, or A
or B choices to your client, etc. That's just a trick.
Some clients are like this, they do need more guidance and expect it from you! They don't always know how to give you the info, sometimes it's hard for them to put their idea in writing or they're not very "visual." Or they write more about their personal life goals or what they ate for lunch than actual instructions because they think that's what you need to "seize" them. When they tell you they're "friendly and bubbly personally who enjoy good chakras people, recycling and the essence of life...", you can simply ask them "So, do you like that blue with that beige or do you prefer this other color palette?" Cut the blabla and ask what you need!
Don't start the projects unless you're a good mind reader or know how to present various samples that will already help your client target what they want!
And when they're slow to respond to your email, write back and ask for
updates in a friendly and professional way (e.g. not pushy.) There's many good tricks for this without looking desperate. Sending an invoice is one of them by the way, when they're not very cooperative and it would fix your issue as well! They usually get back to you quickly!